In a known actuating arrangement of that kind (see the prospectus from the company A. Ott, Kempten, "Mit Prazision zum Erfolg, Ott-Werkzeugspanner", 1986 edition, page 3) the wedge transmission assembly serves in the clamping operation to increase the force which acts on the clamping bar from the spring arrangement in order thereby to enhance the pulling-in force (clamping force) of the tool or workpiece clamping device. In addition the wedge transmission assembly also serves to lock the clamping bar relative to the spindle in the clamped condition, so that in the event of failure of the spring arrangement, for example due to the spring breaking, or in the event of elevated pulling-out forces acting on the tool or the workpiece in opposite relationship to the clamping direction, the component which is clamped by the clamping device is securely held in position. In that known actuating arrangement the piston-cylinder unit serves not only for stressing the spring arrangement and for releasing the collet disposed at the front end of the clamping bar, but also for ejection of the tool from the spindle. As a large part of the force applied by the piston-cylinder unit is used for stressing the spring arrangement, only a part of that force is available for ejection of the tool. In the case of tools with a steep-angle taper, there is now the problem that, at high spindle speeds of rotation, the receiving cone or taper portion of the spindle expands and the tool is drawn further into the receiving cone or taper portion, under the effect of the spring arrangement. Therefore the tool ejection operation involves overcoming a shrink-type fit. In addition at high spindle speeds of rotation the balls are urged under the effect of centrifugal force into the wedge-shaped annular gap between the cone surfaces of the support ring and the clamping ring, whereby the clamping force is unintentionally increased. A higher ejection force is then also required to eject the tool. In order to produce that high ejection force, the arrangement requires a piston-cylinder unit which is of correspondingly large dimensions and/or a high operating pressure for that purpose. If there is a wish to increase the clamping force, that is possible only by increasing the size of the spring arrangement, and that in turn also requires an increase in the size of the piston-cylinder unit and/or an increase in the operating pressure. In order to produce a sufficient clamping stroke movement of the clamping bar in the clamping operation, a spring arrangement of comparatively great structural length is also required. Furthermore in the known clamping device the clamping stroke movement is restricted by the diameter of the balls as the clamping ring bears against the support ring at the end of the release stroke movement. The clamping stroke movement is always somewhat smaller than the ball diameter. The latter cannot be of just any desired size as with an increasing ball diameter on the one hand the structural size of the assembly increases while on the other hand the unintentional increase in the clamping force, which is caused by the effect of centrifugal force, is also increased.
Therefore the invention is based on the problem of providing an actuating arrangement for a tool or workpiece clamping device in a machine tool spindle of the kind set forth in the opening part of this specification, which, while being of reduced structural length for the spring arrangement, has an elevated ejection force, in which there is no unintentional increase in the clamping force due to the effect of centrifugal force, and the clamping stroke movement of which is independent of the ball diameter.